Photoelectric Effect Gizmo

Physics Photoelectric Effect Gizmo

Name(s) ______Date______Hr. ___

Introduction In 1905, Albert Einstein published five papers that revolutionized physics. While today his paper on special relativity is the most famous, it was actually his explanation of the photoelectric effect that earned Einstein the Nobel Prize in 1921.

Einstein's paper validated an idea first suggested by Max Planck, that energy can only be transmitted in tiny packets, or quanta. Einstein extended this idea to light, proposing that light is composed of tiny particles called photons.

Part 1: The Effect of Light on Metal In this activity, you will study the effect light has when it strikes a metal surface. In the Gizmo, set the Intensity to 100%. (To set a slider to a specific value, type the number in the field to the right of the slider and hit Enter.) Be sure that Voltage is set to 0 volts, Show voltage gradient is unchecked, and that Potassium is selected from the dropdown menu. The red dots on the left plate represent electrons on the surface of a potassium slab. If electrons leave the plate, we say they are emitted. If they reach the plate on the right, they can complete a circuit and cause the light bulb to shine.

Set the Wavelength to 400 nm (violet light). Click Flash the light. Describe what occurs afterward.

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Set the Wavelength to 500 nm (green light). Click Flash the light again. How do the results differ from the experiment done with violet light?

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From these observations, do you think light with smaller wavelength has more energy or less energy than light with longer wavelengths?

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Repeat the experiment with different values for Wavelength to find the greatest wavelength that moves electrons from one plate to the other.

biggest = ______

Prior to Einstein's 1905 paper, it was believed that the energy of light was only dependent on its intensity. At the same intensity, red light would have the same effect as green or blue light. Set the Wavelength to 600 nm and the Intensity to 10%.

Click Flash the light. What happened? Were any electrons emitted?

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Increase the intensity and click Flash the light again. Did anything change? Do the photons of light at this wavelength have enough energy to remove electrons?

______Repeat the experiment with a wavelength of 400 nm. What is the effect of intensity on the number of photons produced? On the number of electrons emitted?

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Based on what you have seen, what factor influences the speed of emitted electrons? What factor influences the number of electrons that are emitted?

Speed of electrons is influenced by ______

The number of electrons is influenced by ______

Change the metal selected in the dropdown menu to Calcium, and set the Intensity to 100%. Use the Gizmo to determine the longest wavelength of light that succeeds in causing an electron to cross from one plate to another. Write down your results. Then repeat with Uranium selected. Describe your results.

Calcium: ______Uranium: ______

Which metal requires the shortest wave length of light to emit electrons? ______

Which metal holds onto its electrons most tightly? (Hint: The shorter the wavelength required to remove an electron, the greater the required energy needed to remove an electron.)

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Answer the following two multiple choice questions

What is the effect of doubling the intensity of light on whether electrons will be emitted from a metal?

A. The more intense light is more likely to cause electrons to be emitted than the weaker light B. The more intense light will cause electrons to be emitted with faster velocities than the weaker light. C. The less intense light must shine for a longer time to cause electrons to be emitted. D. Light intensity has no effect on whether electrons are emitted or not.

Green light shines on an unknown piece of metal, and the lab instruments detect emitted electrons. Which of the following will be true if the light is changed to violet?

A. Violet light will cause electrons to be emitted at greater velocities than those removed by green light. B. Violet light will cause electrons to be emitted at lower velocities than those removed by green light. C. Violet light will cause electrons to be emitted only if the light is as intense as the green light. D. It cannot be determined whether violet will cause electrons to be emitted or not.